The present invention relates to a novel shaped article composed of a vinyl chloride (hereinafter referred to as VC) resin having a covering layer comprising a cured organopolysiloxane composition. The invention also relates to a method for the preparation of same.
VC resins belong to a class of the most widely employed thermoplastic synthetic resins for the fabrication of shaped articles of both the hard or rigid type and the soft or flexible type according to the absence or presence of a substantial amount of a plasticizer in the formulation of the molding composition. That is to say, the flexibility and the mechanical strengths, especially, impact strength, of a shaped article composed of VC resins can be improved by formulating substantial amounts of a plasticizer or a rubbery polymeric substance in the molding composition so that the fields of application fields of of the VC resins have been expanded to include medical instruments, wrapping materials for various goods, e.g. foodstuffs, insulating materials for electric wires and cables, materials used in agriculture and construction work and the like.
In order to comply with the requirements of a variety of the application fields above mentioned, above VC resins are usually blended, in addition to the above mentioned plasticizers and rubbery polymeric substances, with various kinds of additives such as fillers, anti-oxidants, ultraviolet light absorbers, anti-static agents, anti-fogging agents, coloring agents, crosslinking accelerators and the like according to the desired properties of the shaped articles.
One of the major problems or defects in the shaped articles shaped out of VC resins is, even setting aside the insufficient heat resistance inherent in VC resins, that the plasticizer and other additives contained therein migrate after a time toward the surface of the shaped article and eventually bleed or bloom on the surface of the article, thus bringing about denaturation or deterioration of the surface layer as well as a loss in the beauty of the appearance of the article with a shortened serviceable life of these articles. Moreover, the bleeding or blooming of the additives on the surface is very disadvantageous from the standpoint of health especially when the additives are toxic or, at least, have unpleasant side effects on the human body. This problem is especially serious when the shaped articles are used in medical applications or come into contact with foodstuffs or drinks.
One of the promising methods of solving the above problems is to provide a coating layer or a covering layer of a polymeric material with no sanitary problems onto the surface of the shaped article of the VC resin.
Among the polymeric materials directed to such a method, organopolysiloxane compositions or so-called silicones such as silicone rubbers belong to the most interesting class of polymers with their high heat resistance as well as their inherent lack of intoxicity to the human body, so that very interesting and useful shaped articles can be obtained if the shaped articles of VC resins are provided with an adequate covering or coating layer of an organopolysiloxane composition.
One of the major difficulties in the above method to obtain a composite product of a VC resin and an organopolysiloxane composition is in obtaining good adhesion between the two two kinds of polymers with so different chemical properties so as to have a satisfactory integration. It is well known that the adhesion of a silicone can be improved by the use of a primer which is applied to the surface before the silicone is bonded thereto. Even with very careful selection and application of a primer, however, no satisfactory adhesion can be obtained between the surface of a VC resin article and an organopolysiloxane composition and, if eventual bonding is obtained therebetween, the adhesive bonding strength is so small and void of durableness that the covering layer of the organopolysiloxane composition readily comes off the surface of the VC resin article with an insignificant pulling or peeling force exerted thereto. Thus no composite products of a VC resin shaped article with a covering layer of an organopolysiloxane composition are available hitherto to the satisfaction of the needs as described above.
The above described problem of poor adhesive bonding between a cured organopolysiloxane composition and the surface of a shaped article of a VC resin is even more difficult to solve with a two-package type room temperature vulcanizable organopolysiloxane rubber than with a one-package type one, the former rubber composition being desirable when larger mechanical strengths are required for the layer of the cured organopolysiloxane composition.